Epoxy resin based systems are widely used as sealing materials, coating compositions, adhesives, and the like, in a variety of fields such as electricity, electronics, and civil engineering and construction. When cured, they exhibit excellent electrical insulating properties, are moisture proof, heat resistant, soldering resistant, chemical resistant, durable, have excellent adhesive properties and mechanical strength. Specific examples include epoxy composite materials using carbon fiber and fiberglass reinforcements, protective coatings for metal surfaces, and protective coatings for concrete, cementitious or ceramic substrates, often referred to as civil engineering applications.
Two part epoxy resin based systems generally include a curable epoxy resin and a curing agent for the epoxy resin. The two components chemically react with each other to form a cured epoxy, which is a hard, duroplastic material. Epoxy resins are substances or mixtures which contain epoxide groups. The curing agents include compounds which are reactive to the epoxide groups of the epoxy resins, such as amines, carboxylic acid, and mercaptanes.
During preparation, one or both of the epoxy resin and curing agent are dispersed or dissolved in a solvent, for example, an organic solvent, to reduce viscosity. Significant environmental and safety concerns are created due to the use of such solvent-based systems since the associated volatile organic compounds (VOCs) create environmental pollution and health hazards.
A variety of epoxy resin curing agents dissolved or emulsified in water have been developed to address the environmental and health concerns. For example: U.S. Pat. No. 4,197,389 discloses a curing agent prepared by reacting at least one polyepoxide compound with at least one polyalkylene polyether polyol to form an adduct which is subsequently reacted with a polyamine; U.S. Pat. No. 5,032,629 describes water compatible polyamine-epoxy adducts prepared by reacting poly(alkylene oxide) mono- or diamines with a polyepoxide to form intermediates which are then subsequently reacted with an excess of a polyamine; U.S. Pat. No. 6,245,835 describes amino-epoxy adduct curing agents prepared by reacting a polyoxyalkylenediamine with a polyepoxide and polyoxyalkylene glycol diglycidyl ether and emulsifying the reaction product in water.
Many current waterborne curing agent and epoxy systems are plagued with problems which limit their usefulness. One problem is cured coatings having poor physical properties, such as hardness, appearance and solvent resistance. Other problems are a relatively high viscosity of the curing agent, making the coatings difficult to apply. Additional problems include a slow cure speed, short pot life and manufacturing difficulties. It is an object of the present invention to provide a novel, low VOC, waterborne curing agent for use with epoxy resin compositions, which overcomes these problems. It is also an object of the present invention to provide waterborne curing agents that, can be easily manufactured, have improved pot life and exhibit low viscosity, even at high solids content.